1. Field of Invention
The present invention relates to a method of fabricating micro- and nano-photonic waveguides based on natural index contrast (NIC) principle for guiding and amplifying optical signal in 1060 nm-1600 nm range. Here a nano-material film of known refractive index (material A) is deposited on a substrate to form a base zone of uniform thickness. Another nano-material film of slightly higher refractive index (material B) is then deposited on top of the base zone. This second material zone, also of uniform thickness, is subsequently patterned to form the core of individual waveguides. A third crust of material A is then deposited on the same substrate on top of the second film that is already patterned into a number of ridges. The patterned layer (material B) thus buried between the first and the third zone (material A) forms the core, while the first and third layers together form the cladding of the waveguide. The whole structure forms a planar waveguide that is suitable for processing and amplifying light in the optical communication range. The present invention also relates to a method whereby the said waveguide serves as the basic element to construct nanophotonic integrated circuit that has application in a number of photonic devices that are important for data-communication, computing, and sensing.
2. Background
Photonic waveguide is the fundamental element for nanophotonic integrated circuits (nPICs) or, in general, photonic integrated circuits (PICs). In addition to PICs, photonic waveguides have a number of applications in sensors, spectrometry, interferometry, and other devices where guided light in a narrow dimension plays a crucial role. For instance, fiberoptic communication systems need highly sophisticated guided wave optical networks. Future high bandwidth, high speed communication environments and the next generation of Internet will need ultracompact, lightweight, low-power, low-loss, and low-cost wavelength division multiplexer, demultiplexer, wavelength router, splitter, coupler, interleaver, optical amplifier, modulator, and other photonic devices. Such technologies in turn require advances in design of ultracompact micro- and nano-photonic structures, with design and engineering of the electromagnetic properties of materials in the scales comparable to the wavelength of information carrying light. Therefore, a capability of fabricating high quality, robust, cost-effective, photonic integrated circuits is important for the next generation fiberoptic communication, computing and sensing.
Photonic waveguides are the basic constituents of photonic integrated circuits (PICs) that are somewhat analogous to the transistors in the electronic ICs. Although the physics of photon (a neutral wave/particle) and electron or hole (charge carrying particles) are different that make an exact comparison between the PIC and electronic IC difficult, nevertheless, waveguides can be designed to process optical signal in as much as transistors can process electronic signals. Confining the focus on photonics for the purpose of present discussion, it is widely known that in the current practice, most photonic components are based on discrete technology where individual elements perform a single function. The thin-film interference filter, also called dielectric thin-film filter (TFF) is an example of a discrete technology; here n-different TFFs are cascaded to demultiplex n-different wavelengths of a multiplexed signal. Because of the discrete nature, the plurality of elements, that are necessary to perform a single function, are assembled together by mechanical means. An example of the situation may be cited again in terms of the TFF. In this case an external fiber carrying the multiplexed signal is interfaced to the TFF by means of a GRIN lens; the method of such interfacing is very complex in itself. The output signal from the TFF again needs to be focused on another external fiber by means of a second GRIN lens. This process needs to be repeated for every wavelength; as a result the discrete technology based modules are bulky, lossy, and performance limited. Moreover, poor yield of the discrete component's assembly process is a cause of their higher cost.
While recently the integrated approach is drawing significant interest, current integrated technologies also suffer from limitations of materials, processing, and performance. For instance, in glass based waveguides, refractive index variation is produced by doping glass with a suitable dopant. The doping is usually done by a diffusion controlled process. Such process is difficult, performance limited and the machineries dedicated to carry out these processes are expensive and not easily amenable for expansion. Other processes such as flame hydrolysis or ion-exchange methods are also complicated, difficult to control, and enjoy partial success. Thus, there is a need to find more efficient methods to produce smarter, robust, and precise photonic waveguides.
The optical waveguides formed on a silicon wafer can be designed to perform many important optical signal processing. A common application is an optical multiplexing and demultiplexing on a chip that is commonly known as photonic integrated circuit (PIC), also as planar lightwave circuit (PLC). A popular application of PICs is an arrayed waveguide grating (AWG) or a reflective arrayed waveguide grating (RAWG). However, waveguides can be designed to perform a number of optical functions such as amplification, modulation, switching, sensing, and other optical signal processing, thus allowing itself to be analogous to a transistor that forms the basis of electronic integrated circuit (IC). Also, using waveguides as the basic building block, a number of PICs can be constructed to carry out various photonic signal processing and the PICs can also be used as a platform for a number of photonic devices essential for fiberoptic communication and computing. Example of such applications includes wavelength router, tunable optical add/drop multiplexer, tunable attenuator, optical interconnect, interleaver, optical power splitter, coupler, and other waveguide based devices.